1. Field of the Invention
This invention relates to a recording medium such as recording paper or the like for use in ink-jet recording or ink-transfer type thermal recording, and more particularly to a recording medium for such purposes which is excellent in ink absorptivity and coloration of image.
2. Description of the Prior Art
Methods of recording by use of recording liquids include, for instance, an old and general method: writing with a fountain pen or the like, and a recently developed method: so-called ink-jet recording. The ink-jet recording system is a recording method in which droplets of recording liquid are generated and expelled by one of various operation principles and applied to a recording medium such as paper or the like to form images. Ink-jet recording is noticed in that it generates less noises and permits high speed printing and multicolor printing. Water-based recording liquids are predominantly used for ink-jet recording in aspects of safety and printability.
For ink-jet recording, ordinary paper has so far been used in general as the recording medium. However, requirements on the medium are growing more severe with improvements in the performance of ink-jet recorders, such as developments of higher speed recorders and multicolor recorders. That is, for securing a high degree of resolution and high quality of images, the ink-jet recording medium must fulfill the following requirements:
(1) It should absorb ink as quickly as possible.
(2) When ink dots overlap one another on the medium, the later ink should not run on the earlier ink dot.
(3) Diameters of ink dots on the medium should not be enlarged more than necessary.
(4) Shapes of ink dots on the medium should be close to true circles and the outlines thereof should be smooth.
(5) Ink dots on the medium should have high optical density and the outlines thereof should not be obscure.
Further, the recording medium for multicolor ink-jet recording must fulfill the following requirements, in addition to the above, in order to achieve image quality comparable to that of color photographs:
(6) It should have a high brightness.
(7) Ink dots of different colors on the medium should each exhibit a good coloration.
(8) Ink absorptivity of the medium should be particularly superior since ink dots of different colors may often overlap one another.
The ink-transfer type thermal recording system has been developed lately, wherein wax-containing colorants (solid inks) are utilized. The recording medium for this recording system also is required to fulfill the above requirements. In particular, it is required when ink dots overlap one another that the earlier-applied dot of ink shall not be molten to diffuse with the heat applied for the next dotting or with the heat contained in the next dot of ink.
However, it is the present situation of the art that no recording medium satisfying all the above requirements has yet been found. As an example, the ink-jet recording paper described in Japanese Pat. Laid-open No. 74304/1977 quickly absorbs ink, but has disadvantages in that ink dots on the paper are liable to be enlarged in diameter and hence the outlines thereof become obscure, and that the dimensional stability of the paper is poor after recording.